This proposal requests a continuation of the project "Latent Path Methodology in Drug Abuse Prevention." Stage-sequential dynamic latent variables play an important role in substance abuse prevention research by developing and refining a measurement methodology for stage-sequential dynamic latent variables. This methodology, called Latent Transition Analysis (LTA), can be used to test models of stage-sequential processes and to construct instruments to measure such processes. The currently funded project has progressed well. The methodological work that was proposed has been completed successfully, and analyses of empirical data now underway, are showing that LTA provides a new, interesting, and uniquely revealing look at prevention data. The proposed research will enhance and expand LTA in a number of areas that will increase its usefulness to the field of substance abuse prevention. During Phase 1 of the proposed research, the LTA procedure will be expanded to include multiple-groups analysis and to compute parameter standard errors. Then the computer program will be amended to make it more user- friendly, and a users' manual will be written. The ultimate aim will be to make LTA available and accessible to prevention researchers. During Phase 2 of the proposed research, an important methodological problem involving model goodness-of-fit testing will be addressed. In Phase 3, we propose to enhance the LTA procedure so that it can base parameter estimation and model testing on incomplete data, as is desirable when a planned missing data design has been used, or when there has been subject attrition or nonresponse. In Phase 4, we propose to expand the LTA procedure so that models can include continuous exogenous predictors, as for example to examine parental influences on the onset process. During all four phases of the proposed research, we will make use of the latest improvements to the LTA procedure to analyze existing substance use prevention data. The LTA procedure is a promising new methodological technique; the proposed research will considerably improve its usefulness to the prevention community. Once the proposed improvements have been made, it will be possible to answer questions about drug abuse onset and what works to prevent it that have been answered before.